Electromagnetic compatibility (EMC) is increasingly becoming a key in the development of electrical motor vehicle propulsion. Since the power requirements of an electrical propulsion chain cannot be fulfilled by conventional low-voltage vehicle electric systems (LV) having a supply voltage of 12 VDC, a traction vehicle electric system is introduced, the voltage level of which is typically in the range of 120 to 1000 VDC. This high-voltage (HV) vehicle electric system connects the energy store, usually placed underneath the luggage space in the rear of the vehicle, to the power converter and a synchronous machine in the engine compartment. Semiconductor components in the pulse inverter switch quickly in order to minimize thermal losses, and consequently, interference pulses with high amplitudes are created which contain high-frequency (HF) spectral components. These can disrupt adjacent electronic systems. The increasing number of sensitive radio services, such as VHF radio, GPS navigation, mobile telephony or driver assistance systems, exacerbates the problem. Systems outside of the vehicle must also not be disrupted; this is regulated in international standards such as CISPR 25 or EU Guideline ECE-R10.
In order to improve the EMC of the electrical propulsion, it is known to design the HV vehicle electrical system to be completely shielded. In this case, individually shielded coaxial cables are used which behave like waveguides in the HF range. These cables perform an impedance transformation of a line termination. Mismatching at the cable ends can lead to reflected disturbance variables and resonance magnifications due to standing waves on the line.
To connect the inverter to the battery, a suitably long shielded cable is required which can, however, endanger the safeguarding of the EMC. On the one hand, high shield currents can occur which, if they are in the high-frequency range, contribute to high emissions and voltage peaks which can even lead to damaging of the inverter or battery. Furthermore, disruptions can be coupled into the vehicle's low-voltage system. The impedance of the electrical and mechanical connection of the cable shield to the shielding of the battery or inverter must be extremely low in order to ensure sufficient shielding. Especially in vehicles, there arise, through vibration or shock, mechanical forces which weaken the shield connection and thus allow the impedance to grow over the long term. Ageing processes, from oxidation or corrosion, can also affect impedance.
The provision of EMC filters between the battery and the inverter is known. Known EMC filters are typically two-wire HV direct current filters which filter out the HF portions in the direct current output, thus reducing the disturbance emissions linked to the line. Furthermore, voltage peaks occur which are elevated through line inductances. In order to prevent a leakage current which results from this, it is known to employ ferrite ring cores, through which the lines are guided.
Such a known filter assembly having several ferrite ring cores is described in DE 10 2013 101 323 A1. The filter comprises a housing body, a first and at least one second bus bar which respectively have a first end section and a second end section, between which there is arranged a middle section. The end sections of the at least two bus bars respectively have terminals for linking electrical conductors to the filter. The first and second end sections and the middle section of the first bus bar are arranged in a first plane and the first and second end sections and the middle section of the at least one second bus bar are arranged in a second plane which is different from the first plane. As a result, the known filter can be connected to the electrical conductors in one mounting direction.
The provision of EMC filters and ring cores at the terminal panels of the battery, however, take up valuable installation space in the motor vehicle. Furthermore, costly connection techniques are required, which make installation more expensive and increase subsequent maintenance costs.